> For the complete documentation index, see [llms.txt](/llms.txt)
# Build items and a shop
Add potions to adventure rewards, then create buttons to use and buy them.
Let players earn one potion along with coins for completing Forest exploration. Using a potion restores 5 stamina, and the shop sells one for 20 coins.
## 1. Register the potion
Store items in a Simple Inventory, which tracks the quantity of each item type. The potion's ID is `potion`.
**Studio**
1. Add **Items** from **Add features**.
2. Under **Tables → Item**, add a row with ID `potion`. Quantity belongs to player data, so do not enter it in this table.
3. Deploy from **Publish → Calculate server differences**, then run **Update the Unity project**.
4. Download the potion use and purchase template.
**SDK (Unity)**
Download the potion storage, use, and purchase template. It contains these settings.
| Setting | Value |
| --- | --- |
| Inventory namespace | `adventure-inventory` |
| Simple Inventory | `Inventory` |
| Item | `potion` |
| Exchange namespace for use and purchase | `adventure-item-actions` |
Deploy the downloaded template through the management console.
1. In the Tokyo region, open **Deploy → Stack list → Create stack**.
2. Name the stack `adventure-items` and select the downloaded JSON file under **Template data**.
3. Click **Create** and wait for **Create complete**.
This creates two exchange recipes in `adventure-item-actions`.
| Exchange name | Consumes | Grants |
| --- | --- | --- |
| `use_potion` | 1 potion | 5 stamina |
| `buy_potion` | 20 free coins | 1 potion |
## 2. Add a potion to Forest exploration rewards
**Studio**
Open `forest` under **Tables → Quests → Quest**. Under **Completion rewards → Add item → Not set**, add the following action. Keep the coin deposit and the mission counter action added on the previous page.
| Field | Value |
| --- | --- |
| Action | `AcquireSimpleItemsByUserId` (inventory) |
| Target resource | None |
| namespaceName | `Inventory` |
| inventoryName | `Inventory` |
| userId | `#{userId}` |
Add one entry to **acquireCounts**, with `itemName = potion` and `count = 1`. Save, deploy to the server, and update the Unity project.
**SDK (Unity)**
Open the template used for `adventure-game`. Append the following entry to `forest` → `contents → completeAcquireActions`. Keep the coin deposit and mission counter entries.
```yaml
- action: Gs2Inventory:AcquireSimpleItemsByUserId
request: |-
{"namespaceName":"adventure-inventory","inventoryName":"Inventory","userId":"#{userId}","acquireCounts":[{"itemName":"potion","count":1}]}
```
Open **Deploy → adventure-game → Update stack**, select the edited file under **Template data**, and update. Wait for **Update complete**.
## 3. Add quantity, use, and purchase controls in Unity
Stop Play Mode. Adding the following file changes the right panel to show potion quantity and action buttons. Keep the adventure panel on the left.
**Studio**
Create an empty GameObject named `Extensions`. Keep the login and mission reward buttons on the adventure screen.
Place AdventureItems.cs in `Assets/AdventureExtensions`, then add **Adventure Items** to `Extensions`. It uses the signed-in `Gs2ClientHolder` and `Gs2GameSessionHolder`.
**SDK (Unity)**
Uncheck **Adventure Daily** on `Extensions`.
Place AdventureItems.cs in `Assets/AdventureExtensions`, then add **Adventure Items** to `Extensions`. Assign the scene's `AdventureLogin` to **Login**.
Widen the Game view so the adventure panel on the left and potion panel on the right are both visible. Enter Play Mode, log in, and check that the potion quantity appears.
Subscribe to `SimpleInventory("Inventory").SimpleItem("potion")` to display the quantity. The same callback receives the initial value and subsequent changes.
```csharp
var item = Client.Inventory.Namespace(InventoryNamespace).Me(Session)
.SimpleInventory("Inventory").SimpleItem("potion");
var id = await item.SubscribeWithInitialCallAsync(value => potion = value);
```
Start and complete Forest exploration on the left. If the potion count on the right increases by one and coins increase on the left, the new reward is working. After deployment, reward changes can take up to five minutes to take effect. If only coins increase, wait a little, then start and complete another forest quest. Continue checking coins and stamina in the left panel.
## 4. Use a potion
With stamina at 15 or below, click **Use 1 potion to restore 5 stamina**. The potion count decreases by one and stamina increases by five. Any natural recovery during the operation is added too.
The use button calls the following exchange through `RunWrite(id => Exchange("use_potion", id))`. `requestId` is the key used to retry the same operation after a connection error.
```csharp
private async UniTask Exchange(string rate, string requestId)
{
var transaction = await Client.Exchange.Namespace("adventure-item-actions").Me(Session).Exchange()
.ExchangeAsync(rate, 1, speculativeExecute: false, duplicationAvoider: requestId);
if (transaction != null) await transaction.WaitAsync(all: true);
}
```
The template uses `Gs2Inventory:ConsumeSimpleItemsByUserId` to consume the item and `Gs2Stamina:RecoverStaminaByUserId` to grant stamina. Also try the use button with zero potions. An insufficient-items error appears and stamina does not increase.
## 5. Buy a potion with coins
With at least 20 coins, click **Buy 1 potion for 20 coins**. Coins decrease by 20 and potions increase by one.
The purchase button uses the same exchange API with the exchange name changed to `buy_potion`.
```csharp
RunWrite(id => Exchange("buy_potion", id)).Forget();
```
The purchase consumes coins with `Gs2Money2:WithdrawByUserId`, using `slot = 0`, `withdrawCount = 20`, and `paidOnly = false`. It grants one `potion` with `Gs2Inventory:AcquireSimpleItemsByUserId`.
Stop and restart Play Mode, then log in as the same player. Check that the purchased potion is still there before moving on to characters.
[Next: Collect and train characters]()